176 FLIGHT
THE combustion chamber consists of an inner
' chamber and an outer shell. The inner
chamber is a mild-steel forging, machined all over
and chromium plated. The outer case is cast in
aluminium alloy Q.T.D.133, and is made in two
portions which fit over the inner chamber. The outer
case incorporates an integral scroll along which
passes methanol fuel rcgeneratively to cool the
inner chamber. A dump valve is also fitted to drain
the outer chamber; normally in the open position, it
is closed only by the application of full methanol
pressure during firing.
The gearbox for the pumps is driven by a shaft
with two universal couplings which permit limited
relative movement between the box and the source
of power. The drive Is geared up by an epicyclic
gear of about 2.7:1 ratio, the outer annulus of
which is normally free to rotate, so isolating the
pumps from the input shaft, the latter being driven
at all times. When the pilot closes the master
switch a nitrogen-operated piston clamps the band
clutch, so arresting the rotation of the annulus gear
and causing the pumps to rotate. The train of spur
gears drives the fuel and oxidant pumps and an oil
pump.
The liquid-oxygen pump has a fully shrouded
centrifugal impeller, cast in phosphor-bronze and
machined all over. The case is made of aluminium
alloy, with inserted stainless-steel rubbing strips
beside the impeller. The seals are either of leather
or else of Gaco, which offers the advantage of
being proof against special lubricants. The metha-
nolfwater pump has an unshrouded steel centrifugal
impeller, with a separately made entry helix.
PROPELLANT PUMP
GEAR BOX
DRIVE
FLANGE
LIQUID OXYGEN
PUMP
FUEL
PUMP
Delivery pressure varies between 500 and
700 Ib/sq in.
The control valves are, as far as possible, grouped
into two compact banks. The valves are nitrogen-
operated poppet-type units, with streamline heads
and a very low pressure-drop. The valves and
pistons are of light alloy, and the seats are of soft
aluminium. The gas-sealing packing is of leather.
BY-PASS
VALVE
ARMSTRONG SIDDELEY SN
THE term "rocket" is applicable to any device which produces a propulsive jet by the combustion or dissocia tion of one or more fuels, without the combination of
oxygen from the atmosphere. Although fundamentally the
simplest form of propulsion unit imaginable, the rocket can
assume any of a great variety of forms.
The simplest unit of all is the solid-fuel rocket of the November 5th variety, in which a rigid case is filled with a combustible
mixture containing all the ingredients necessary for the produc tion of the jet. Solid-fuel motors were made by the million for
unguided missiles during the 1939-45 period, and are also manu factured for take-off-assistance installations for many types of
aircraft and missiles. There is also the liquid-fuel rocket which, according to the size of tank fitted, can have variable burning
time—and can also be throttled and shut down. The fuel, or fuels, can conveniendy be fed into the combustion, or reaction,
chamber merely by pressurizing the tanks with a sqpply of com pressed air or inert gas.
If a rocket is required capable of acceptance for a piloted air craft on the same basis as are the more established forms of
aircraft power unit, something more refined is necessary. For example, it is preferable that the fuels should fete fed by pumps; a
foolproof control system is a "must"; aiyf it is also highly desirable that the unit should have a hfe,/at least measured in
hours and not minutes. /
Ignoring the take-off-assistance application, for which a short-duration, expendable unit is adequate rockets can be applied to
aircraft either as boosters for limited periods when extra power is
needed or else they can be the primary propulsion unit, i.e., the aircraft can be powered solely by the rocket motor. The charac
teristics of all rockets are such that, unlike all other forms of aero engine, they provide thrust that does not decrease with
increasing altitude; in fact, it actually increases. Consequendy, a rocket can provide an extremely effective booster unit where
rate of climb and high-altitude performance are of paramount importance—as they are on all types of fighter aircraft. Rocket-
thrust can provide valuable assistance, also, in rapidly accelerating a supersonic aircraft through the speed of sound.
Where duration is of minor consequence, there is also a case for the all-rocket fighter; but it is still too early to discuss the
applications of rocket motors which are being developed in this country, and the following account must be treated simply as a
chronicle of the development of the first British aircraft rocket (except, that is, for assisted take-off units), with a security veil
drawn over all that has come after it.
, ft was in 1946 that the Ministry of Supply asked Armstrong Siddeley Motors, Ltd., of Coventry, to develop a liquid-fuel
rocket motor with a mrust of 2,000 lb for use as a booster unit for fighters. The company began rocket work at the end of thai
year, with Mr. S. Allen, the experimental engineer in charge of all combustion research, at the head of the new team. His first
two recruits were Mr. D. Hurden and Mr. H. L. G. Sunley.
From the outset, the company were working virtually from scratch. The only closely related work going on in Great Britain
at that time was that undertaken by the M.o.S. itself, at the R.A.E. out-station at Westcott. The country furthest advanced
in the rocket field was certainly Germany, and Mr. Sunley was, in fact, in Germany with the M.o.S. when he joined Armstrong
Siddeley. When he returned, he brought with him numerous reports and selected items of research equipment. The company's
engineers began by holding discussions with the R.A.E. and with any other organization who had any experience of liquid-fue!
rocketry, and these early talks led to the abandonment of kero-sine as the proposed hydrocarbon fuel, the eventual choice being
liquid oxygen and a 65/35 per cent mixture of mediyl alcohoi (methanol) and water.
Gradually, the form of the new rocket began to crystallize; there was, however, nowhere that these ideas could be put to the
test. The development of small combustion chambers was con-